Between 15-20,000 years ago, how did humans spread from Asia to North America?

the Bering Ice Bridge saw the migration of Asians into North America

Explanation:

answer; /// the correct answer is evidence of the olmec civilization has been found in southern american in a hot steamy forest, archaeologists have found earthen artifacts at several sites that were evidence of the olmec civilization. these   artifacts were mounds,courtyards and pyramids build of stones, also on top of the mounds were many monuments made of stone, some of these stone structures are very large, they weigh as much as 44